Abstract: Seagrass leaf litter has been proved to be the main source of chromophoric dissolved organic matter (CDOM) in seagrass beds and CDOM released from seagrass leaf litter is greatly influenced by salinity. According to the salinity range in Xincun Bay, Hainan, China, a salinity gradient (0, 11, 22, 33) was set to study the effects of salinity on CDOM released by leaf litter of two types of seagrass (Enhalus acoroides and Thalassia hemprichii). The results showed that CDOM was rapidly degraded under ultravioletB in four salinity conditions, and significantly higher CDOM and lower DOC photodegradation rates of E. acoroides leaf litter were found under low salinity (0) than under the other three salinity levels. However, no significant difference in organic components of CDOM such as proteinlike and humiclike substances was found during photodegradation for both seagrass species under these four salinity levels. The photodegradation of dissolved organic nitrogen (DON) released by E. acoroides was intensely promoted under 0 salinity. Especially, 26.44% of DON was photodegraded to dissolved inorganic nitrogen (DIN), of which 94.32% was converted to ammonium. However, no obvious effect of extremely low salinity was found on the photodegradation of DON released by T. hemprichii. Therefore, extremely low salinity would influence the photodegradation of CDOM and accelerate the conversion rate from DON to DIN released by E. acoroides, which may change carbon and organic nitrogen cycle in seagrass beds.